1. Field of the Invention
The present invention relates to a capacitor parts and, more particularly, a capacitor parts applicable to a decoupling capacitor provided to a circuit substrate, on which high-speed semiconductor chip, etc. are mounted, to stabilize a power supply voltage and to reduce a high-frequency noise.
2. Description of the Related Art
In recent years, in the digital LSI typified in the microprocessor, a reduction in a power supply voltage made by an increase in a processing speed and a reduction in a consumption power is proceeding. In such digital LSI, the power supply voltage is prone to become unstable when the impedance of the LSI is varied abruptly, or the like. Also, since a stable operation in a further high frequency (GHz band) range is required of the high-speed digital LSI, it is needed to prevent the malfunction of LSI caused due to the high-frequency noise.
Therefore, for the purpose of stabilizing the power supply voltage and reducing the high-frequency noise, the decoupling capacitor is arranged between a power supply line and a ground line of the LSI in the circuit substrate.
As such decoupling capacitor, in Patent Literature 1 (Patent Application Publication (KOKAI) Hei 11-68319) and Patent Literature 2 (Patent Application Publication (KOKAI) 2003-68923), the method of forming the decoupling capacitor to be built in the multi-layered circuit substrate is set forth.
As the characteristic of the decoupling capacitor, the characteristic having a sufficiently low impedance in a wide high-frequency band is desired. However, since the capacitor parts has ESL (Equivalent Series Inductance), the impedance is increased in a frequency range that is higher than a resonance frequency as the frequency is increased. Thus, the high-frequency band in which the impedance is kept still low is narrowed.
As the measure against this defect, such an approach is taken that a plurality of capacitor parts each having a different impedance mutually are mounted onto the circuit substrate to be connected electrically in parallel, so that the impedance can be reduced in the wide high-frequency range by the synthesized impedance.
However, in case a plurality of capacitor parts are mounted onto the circuit substrate, the routing of leads is required between the LSI chip and the capacitor parts and thus relatively large parasitic inductances exist between these leads. Also, even though a wiring distance between the LSI chip and the decoupling capacitor is set shortest by arranging the decoupling capacitor immediately under the LSI chip, there is a limit to a reduction in the parasitic inductance, and thus it is extremely difficult to reduce the impedance in the wide high-frequency band (GHz band).